Mobile communication systems typically do not perform as well as wired communication systems when handling large amounts of data. IMT-2000 is a wireless communication system designed to enable large capacity data communication.
The universal mobile telecommunications system (UMTS) is a third generation mobile communication system evolved from the European Global System for Mobile Communications (GSM) and aims to provide improved mobile communication service based upon a GSM Core Network and Wideband Code Division Multiple Access (W-CDMA) wireless connection technology.
In December 1998, the ETSI of Europe, the ARIB/TTC of Japan, the T1 of the United States, and the TTA of Korea formed the Third Generation Partnership Project (hereinafter, referred to as “3GPP”), which is currently creating a detailed specification for standardizing the UMTS.
The work towards standardizing the UMTS performed by the 3GPP has resulted in the formation of five technical specification groups (TSG), each of which is directed to forming network elements having independent operations.
Each TSG develops, approves, and manages a standard specification in a related region. Among them, a radio access network (RAN) group (hereinafter, referred to as “TSG-RAN”) develops a specification for the function, items desired, and interface of a UMTS terrestrial radio access network (hereinafter, referred to as “UTRAN”), which is a new RAN (i.e., radio interface) for supporting a W-CDMA access technology in the UMTS.
FIG. 1 is a block diagram illustrating a UMTS network structure.
Referring to FIG. 1, the UMTS comprises a terminal (or User Equipment (UE)), a UTRAN 100 and a core network (hereinafter, referred to as “CN”) 200.
The UTRAN 100 includes one or more radio network sub-systems (hereinafter, referred to as “RNS”) 110, 120. Each RNS 110, 120 includes one radio network controller (hereinafter, referred to as “RNC”) 111 and a plurality of base stations (hereinafter, referred to as “Node-Bs”) 112, 113 managed by the RNC 111. One or more cells exist for each Node B.
FIG. 2 is a diagram illustrating a radio protocol architecture used in the UMTS.
Referring to FIG. 2, the radio interface protocol is horizontally formed of a physical layer, a data link layer and a network layer. The radio interface protocol is vertically divided into a user plane for transmitting data information and a control plane for transmitting a control signal. The user plane is a region in which traffic information of a user, such as voice or an Internet-protocol (IP) packet, is handled. The control plane is a region in which control information, such as an interface of a network or maintenance and management of a call, is handled.
In FIG. 2, protocol layers may be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based upon the lower three layers of an open system interconnection (OSI) model well-known in the field of telecommunications.
Each layer shown in FIG. 2 will now be described.
The first layer (L1), that is, the physical layer, provides an information transfer service to the upper layer by using a physical channel. The physical layer is connected via a transport channel to a medium access control (hereinafter, referred to as “MAC”) layer which is an upper layer. Signals are transferred between the MAC layer and the physical layer through the transport channel.
The L2 layer includes the MAC layer and a Radio Link Control (RLC) layer.
The MAC layer provides a re-allocation service of the MAC parameters for allocation and re-allocation of radio resources. The MAC layer is connected to the radio link control (RLC) which is an upper layer through a logical channel. Various logical channels are provided according to the kind of transmitted information. In general, when information of the control plane is transmitted, a control channel is used. When information of the user plane is transmitted, a traffic channel is used.
The RLC layer supports a reliable data transmission and may perform a function of segmentation and concatenation of an RLC service data unit (SDU) coming from a higher layer.
The L3 layer has a radio resource control (RRC) layer at a lowermost portion.
The RRC layer is defined in the control plane, and handles the controlling of logical channels, transport channels, and physical channels related to establishment, reconfiguration, and release of radio bearers (RBs). A RB service signifies a service provided by the second layer (L2) for data transmission between the terminal and the UTRAN. In general, establishment of the RB refers to the processes of stipulating the characteristics of a protocol layer and a channel, which are required for providing a certain service, and setting the respective detailed parameters and operation methods.
Hereinafter, an Multimedia Broadcast/Multicast Service (hereinafter, referred to as “MBMS”) will be described in detail.
The MBMS refers to a method for providing a streaming or background service to a plurality of terminals by using MBMS bearer services only for the downlink. An MBMS service includes one or more sessions, and MBMS data is transmitted to the plurality of terminals through the MBMS bearer service only when the session is ongoing.
The UTRAN 100 provides an MBMS bearer service to a terminal using a radio bearer. There are two types of the MBMS radio bearers (RB) used by the UTRAN 100, a point-to-point RB and a point-to-multipoint RB. The point-to-point RB is a bi-directional RB, and includes a DTCH (dedicated traffic channel) as a logical channel, a DCH (dedicated channel) as a transport channel, and a DPCH (Dedicated Physical Channel) or a SCCPCH (Secondary Common Control physical Channel) as a physical channel. The point-to-multipoint RB is a uni-directional downlink RB, and includes, as shown in FIG. 3, an MTCH (MBMS Traffic Channel) as a logical channel, an FACH (Forward Access Channel) as a transport channel, and an SCCPCH as a physical channel. The logical channel MTCH is configured for each MBMS service provided to each cell, and is used to transmit user plane data of a certain MBMS service to a plurality of terminals.
The logical channel MCCH (MBMS Control Channel) of FIG. 3 is a point-to-multipoint downlink channel and is used to transmit control information related to the MBMS. The logical channel MCCH is mapped to the transport channel FACH (Forward Access Channel), and the transport channel FACH is mapped to the physical channel SCCPCH (Secondary Common Control Physical Channel). One MCCH may exist for each cell.
A UTRAN providing an MBMS transmits MCCH information to a plurality of terminals through an MCCH. Here, the MCCH information includes an RRC message related to the MBMS. For example, the MCCH information includes service information for indicating every MBMS service available in the present cell, MBMS Radio Bearer Information indicating set up information of a point-to-multipoint RB, or access information indicating that an RRC connection is requested for a certain MBMS service.
FIG. 3 is a diagram illustrating a channel mapping for a point-to-multipoint service. FIG. 4 is a diagram illustrating a transmission of control information.
Referring to FIG. 4, MCCH information is periodically transmitted according to a modification period and a repetition period. The MCCH information is divided into critical information and non-critical information. The non-critical information may be freely modified and transmitted at each modification period and repetition period. However, the critical information may be modified and transmitted only at each modification period. That is, the critical information is repeated once and transmitted at each repetition period, and transmission of the modified critical information only at the beginning of a modification period. The critical information includes, for example, the above-described service information and radio bearer information, and the non-critical information includes the access information. Only the access information may be transmitted by an exclusive period. The exclusive period by which the access information is transmitted is called an access period. The length of the access period is the same length or shorter than the repetition period. The repetition period may be expressed as a multiple of the access period, and the modification period may be expressed as a multiple of the repetition period.
The MCCH transmits “change information” at the beginning (head) of the corresponding modification period to assert how the MCCH information that is changed (updated) for a modification period corresponds to a MBMS service. The change information includes at least one MBMS service identifier related to the changed control information. Accordingly, a terminal receiving the MCCH receives the change information transmitted at the beginning of the corresponding modification period first, and then, if an identifier of the MBMS service to which the terminal has joined is included in the change information, the terminal receives MCCH information for the corresponding modification period. The change information is not transmitted at each repetition period but is transmitted only at the beginning of the corresponding modification period.
The UTRAN periodically transmits a physical channel MICH (MBMS notification indicator channel) in order to inform whether MCCH information is changed or not in a modification period. A change to the MCCH information refers to the generation, addition, modification and/or deletion of a certain item of the MCCH information. When a session of a certain MBMS service starts, the UTRAN transmits, via the MICH, an NI (notification indicator) during a certain modification period in order to notify the terminal wishing to receive the certain MBMS service that it should receive the MCCH.
A terminal which does not receive an MTCH but has joined a certain MBMS service periodically receives the indicator NI through the MICH. The terminal receives the change information of the MCCH for a modification period that follows the certain modification period, if the received NI indicates a change to MCCH information related to the certain MBMS service. After receiving the change information, the terminal continues to receive the MCCH information for the corresponding modification period when an identifier of the MBMS service which the terminal has joined is included in the change information.
On the other hand, a terminal which is already receiving the MTCH and has joined a certain MBMS service receives the change information once at each modification period. After receiving the change information, the terminal continues to receive MCCH information for the corresponding modification period if an identifier of the MBMS service which the terminal has joined is included in the change information. Since the terminal periodically receives the change information from the previous modification period, the terminal may recognize whether the MCCH information related to the service (e.g., the service that the terminal has joined) has changed or not by receiving only the change information periodically.
Because of a cell transition, a terminal which does not receive MCCH information at the previous modification period may recognize whether MCCH information related to the service has changed or not by receiving service information at the next modification period. As described above, the change information indicates an identifier of the MBMS service related to the MCCH information which is modified for the present modification period for the present cell. The service information, however, indicates an identifier of every MBMS service available in the present cell. Accordingly, the terminal which has not previously received the MCCH information must receive service information in order to determine a state (status) of every MBMS service available in the present cell.
A terminal that intends to receive a certain MBMS service using a point-to-multipoint RB receives MCCH information including radio bearer information through an MCCH and establishes the point-to-multipoint RB in the terminal using the information. After establishing the point-to-multipoint RB, the terminal continues to receive the physical channel SCCPCH to which the MTCH is mapped and therefore acquires certain MBMS service data transmitted through the MTCH.
A terminal having received the MCCH information in the previous modification period in the related art may recognize whether the MCCH information related to the service (that the terminal has joined) has changed or not by receiving only the change information at the next modification period. On the other hand, a terminal which has not received the MCCH information at the previous modification period because of a cell transition or the like may recognize that the MCCH information has changed or not by receiving service information at the next modification period. Accordingly, the UTRAN provides change information and service information at the same time for a single modification period.
The change information indicates an MBMS service identifier related to MCCH information which is changed for the present modification period in the present cell, while service information indicates an identifier of every MBMS service available in the present cell. Therefore, the identifier of the MBMS service related to the MCCH information which is changed for the present modification period is unnecessarily repeated in the change information and the service information. Accordingly, in the related art change information transmitting method, the MCCH transmission may waste resources.
Furthermore, unlike the other MCCH information, which is repeated and transmitted, the change information in the related art is transmitted only at the beginning of a modification period. In such a case, a problem may arise with respect to the reliability of the reception of the change information. In addition, when the terminal does not receive the change information, the terminal must receive every MCCH information which is transmitted thereafter.